The present invention relates to the field of printing with waterborne inks on substrates, especially non-porous substrates, to coating compositions which can condition such substrates for high definition printing with waterborne inks, substrates coated with such compositions capable of receiving aqueous ink, methods of coating the substrates with the coating compositions so as to improve the ability of the substrate to receive waterborne ink, and methods of printing with waterborne inks on coated substrates.
Printing with waterborne inks on non-porous substrates presents well known problems, for example bleeding, which is related to wettability. If the non-porous substrate is too hydrophobic, waterborne inks tend to dewet or retract. If the non-porous substrate is too hydrophilic, waterborne inks tend to spread. In either case, the resultant printing problem will be referred to herein as “bleeding,” and is a problem to which the present invention is directed.
In addition, the use of water-based inkjet inks on non-porous substrates such as plastics is known to be very problematic due to wetting problems as well as slow drying, which for non-absorbent surfaces has to occur only by evaporation. Others have suggested using polyvinyl alcohol as a coating for such substrates and including hydrophilic silica gel. Polyvinyl alcohol and pigments such as titanium dioxide for suitable substrate coatings have been suggested. Salts of high molecular weight carboxylic acids which lock the aqueous dye based inks into the surface by ionic interaction have also been suggested.
In spite of all the prior attempts at solving this problem, there remains a long-felt need in this art for a way to condition non-porous surfaces to receive waterborne ink in high definition, with low or no bleeding. It is therefore an object of the present invention to provide improved coatings for substrates to be printed with waterborne ink formulations.
It is a further object of the invention to provide substrates which are suitable for aqueous ink jet printing processes.
Another object is to provide waterborne ink jet printing objects such as paper or plastic.
A further object is to provide a method of printing on hydrophobic media such as polyethylene terephtalate, polyester, polyamide, polypropylene, and the like, with water-based inks.